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  <title>Document</title>
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  <script>
    /* 
    1. 更新元素 7
        push / unshift / pop / shift / splice / sort / reverse 
    2. 遍历相关 8
        forEach / filter / map / reduce / every / some / find / findIndex
    3. 其它  5
        indexOf / includes / concat / join / slice
    */

    products.sort((p1, p2) => {
      return p2.price - p1.price
    })

    products.map(p => ({...p, name: 'abc'}))
    cart.reduce((pre, item) => pre + item.price * item.count, 0)

    Array.__proto__
  </script>
</body>
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